1. Field of the Invention
The present invention relates to an optical apparatus having a focus adjusting function capable of detecting the focus in each of a plurality of areas in an image plane, and to a focus adjustment control circuit.
2. Related Background Art
In the case of a camera which can detect a focus in, or measure a distance to, each of a plurality of focussing areas, if a lens is driven in accordance with the focus or distance of an object in the focus area at the nearest distance determined from a plurality of focus detecting or distance measuring results, a correct auto focussing operation is often impossible. To solve this problem, an algorithm is disclosed in U.S. Pat. No. 5,121,151 in which, for example, if the focus detecting or distance measuring results of three points show a specific pattern such as "far", "middle", and "near", the focus area of "middle" is selected (because "near" may be the ground).
Another apparatus is disclosed in U.S. Pat. No. 4,749,848 which can detect a defocus amount in, or measure a distance to, an arbitrary point in an image space by detecting a focus in, or measuring a distance to, each of a number of focus areas in an image plane.
This proposed apparatus will be described by taking as an example photographing a scene, such as is shown in FIG. 6.
An image plane is divided into fine blocks (sets of a plurality of pixels on an area sensor), and the distance to or the focus of each block is measured to obtain distance distribution information or defocus amount information, such as shown in FIG. 7. Objects constituting the image space are grouped in order to determine the object layout in the image space.
FIG. 8 shows an example of the results of grouping performed in accordance with the distribution data shown in FIG. 7. Grouping defines the area of each object. Several practical grouping methods are known. An example of the simplest method is to judge that two adjacent blocks constitute the same object if the difference of the distance or the defocus between the two blocks is a predetermined value or smaller. This judgement is performed for each of adjacent two blocks.
By using a grouping method, the focus areas are grouped for each object constituting the image space such as is shown in FIG. 8.
The area of a main object among the objects constituting the image space is determined in accordance with, for example, distance information (or defocus amount information), size information of each object, position information of each object in the image plane, and the inclination extent of each object or the like.
Another grouping method uses a histogram of distance distribution (or defocus amount distribution). Several focussing methods are also used. In one method, attention is paid only to the nearest object and the most frequently occurring distance. If the distance difference therebetween is very small, the middle area between the two objects is focussed, whereas if not, the front object is focussed.
However, in a practical auto focussing operation, focus detection or distance measurement is not always performed correctly for all focus areas, and the distance distribution (or defocus amount distribution) changes with an error of the distance measurement (or focus detection) and with a fine motion of a photographer or an object during auto focussing. Furthermore, with a TTL (through the (taking) lens) type focus detection system, a stop position of a taking lens, when the focus is detected, may greatly influence the detected focus. Particularly, when a distance distribution (or defocus amount distribution) is repetitively measured during focus adjustment, the obtained distance distribution (or defocus amount distribution) changes minutely each time it is measured. Although this phenomenon poses no practical problem if the objects are spaced apart from each other such as shown in FIG. 6, it becomes conspicuous if objects are near to each other or a distance of a main object from the background is short.
FIG. 9A shows an example of such a scene wherein two persons stand side by side just in front of a wall. FIG. 9B shows a focus detecting area (or distance measuring area) of focus detecting means for adjusting the focus of this scene. FIGS. 10A to 10D show defocus maps representing defocus distributions measured with such a focus detecting system.
FIG. 10A shows an example of a division into four groups. Groups A1 and A2 are approximately the groups of the left person shown in FIG. 9A, and groups A3 and A4 are the groups of the right person shown in FIG. 9A. In this case, most of the background wall is recognized as a group from which focusses are not detected (in FIG. 10A, blank blocks). FIG. 10B shows an example in which the persons are correctly discriminated as groups B1 and B2. In FIG. 10C, the two persons are recognized as one group C3, and the wall and part of the persons are recognized as other groups (refer to groups C1 and C2). In FIG. 10D, the two persons and part of the wall are recognized as the same group D2, and only part of the persons is recognized as another group D1.
As above, even if the same scene is photographed, the distance distribution (or defocus amount distribution) becomes very different depending upon the position of a taking lens and an enabled/disabled state of focus detection.
If the focus adjustment is performed by repetitively determining a focus area from such different distance distributions (or defocus amount distributions), the focus area cannot be determined. Therefore, hunching or the like may occur or the focus area changes each time the focus adjustment is performed, so that the photographer loses confidence in the camera.
Some conventional cameras of the type that a focus of each of a plurality of focus areas in an image plane can be detected, display the focus detection results. For example, in Japanese Patent Application Laid-Open No. 8-286253, the positions of all focus detectable areas and an in-focus state of each area can be visually recognized at once by changing the color of each segment of a display.
However, with Japanese Patent Application Laid-Open No. 8-286253, since color display is performed for all focus detectable areas, this color display is superposed upon objects so that the objects are hard to be visually recognized.
For example, if an area c10 shown in FIG. 18B is focussed, the distance measuring areas or focus detecting areas at the same distance also become in-focus. The color display is therefore made in these areas in the baby face. Although the in-focus area can be recognized, the object becomes hard to visually recognize and photographing is hindered. Also, the area actually focussed cannot be identified.
Furthermore, if in-focus states are displayed for all the distance measuring or focus detecting areas, the distance measuring or focus detecting areas of a further object at the same distance to the main object is also displayed as being in the in-focus state so that the photographer may think that the object different from the main object was focussed inadvertently.
For example, if the area b3 of a human face shown in FIG. 18A is focussed, the street lamp at the same distance is also in an in-focus state and an in-focus display is made. In this manner, if all the distance measuring or focus detecting areas in an in-focus state are displayed, the photographer cannot judge whether the person was focussed or the street lamp was focussed, or the photographer may erroneously judge that the street lamp was focussed.